BioCryst
Pharmaceuticals, Inc. (NASDAQ:BCRX) today announced
proof-of-principle data demonstrating that BCX4430 is efficacious and
well tolerated in a preclinical disease model for evaluating efficacy
against yellow fever virus infection. BCX4430 is the lead compound in
BioCryst’s broad-spectrum antiviral (BSAV) research program. The
objective of BioCryst’s BSAV program is to develop broad-spectrum
parenteral and oral therapeutics for viruses that pose a threat to
national health and security.

A presentation entitled “BCX4430, an adenosine analog, with potent
activity against yellow fever virus in a hamster model,” will be
presented by Dr. Justin Julander at the 2nd Antivirals Congress in
Cambridge, MA today at 5:10PM E.T.

These studies comprehensively evaluated the efficacious dose, dose
duration, and therapeutic use of parenteral BCX4430 in the treatment of
yellow fever infection. Syrian Golden Hamsters–a widely accepted model
for establishing efficacy against yellow fever —virus were inoculated
intraperitoneally with ten times the cell culture infectious dose (CCID50)
of yellow fever virus (Jimenez strain) and treated parenterally with
BCX4430 administered either once or twice daily for 4 to 7 days. In
studies with treatment just prior to infection or delayed up to 4 days
after infection, BCX4430 treated animals had significantly (p<0.001)
improved survival (80–100%) compared to animals receiving saline placebo
(20-30%). It is important to note that in this model, serum viral titers
peak at day four after infection, indicating that BCX4430 has the
potential to be an effective therapeutic when administered as
pre-exposure prophylaxis; as post-exposure prophylaxis during the virus
incubation period; and as a treatment during the prodromal period and
symptomatic disease. Treated animals also exhibited significantly lower
viral titers in serum, improved weight gain, and decreased liver damage
as measured by lower levels of alanine transaminase and aspartate
transaminase.

In addition, BCX4430 demonstrated a wide therapeutic index of 50 with a
minimum effective dose of 4 mg/kg/day (p<0.05 vs control), as measured
by survival, and a maximum tolerated dose of 200 mg/kg/day, as measured
by percent weight change.

The study was conducted under the National Institute of Allergy and
Infectious Diseases’ (NIAID’s) Animal Models of Infectious Disease
Program. Dr. Justin Julander of Utah State University, who coordinates
yellow fever testing under the NIAID Program stated, “BCX4430 is an
exciting, potential antiviral therapy for the treatment of yellow fever
virus infection, for which no approved treatment currently exists. The
level of efficacy observed for BCX4430 in these studies compared to
other antivirals evaluated against yellow fever is exceptional. BCX4430
warrants further study and development as a potential human therapeutic.”

“BioCryst’s BSAV research program has generated convincing evidence of
efficacy in preclinical studies, not only in the yellow fever model, but
also against other viruses studied in vitro and in vivo.
BCX4430 represents an exciting research stage project that could become
a breakthrough for the treatment of hemorrhagic fevers caused by
flaviviruses and filoviruses. These viruses are viewed by U.S.
Government Agencies as high priority targets for development of medical
countermeasures,” said Dr.
William P. Sheridan, Senior Vice President & Chief Medical Officer
of BioCryst Pharmaceuticals. “We are seeking government funding to
support development of BCX4430 as a medical countermeasure for the
protection of civilian and military populations, and plan to announce
additional data from the BSAV program in upcoming publications and at
scientific conferences.”

About the BSAV Program & BCX4430

The objective of BioCryst’s BSAV research program is to develop
broad-spectrum parenteral and oral therapeutics for viruses that pose a
threat to health and national security. The lead BSAV compound is
BCX4430, an RNA dependent-RNA polymerase inhibitor that has demonstrated
broad-spectrum activity in multiple viruses and a favorable preliminary
preclinical safety profile. BioCryst plans to develop these compounds in
collaboration with US Government Agencies following the Animal Rule
regulatory pathway.

About BioCryst

BioCryst Pharmaceuticals designs, optimizes and develops novel small
molecule drugs that block key enzymes involved in infectious and
inflammatory diseases. BioCryst currently has two late-stage development
programs: peramivir, a viral neuraminidase inhibitor for the treatment
of influenza, and ulodesine (BCX4208), a purine nucleoside phosphorylase
(PNP) inhibitor for the treatment of gout. In addition, BioCryst is
developing two preclinical compounds: BCX5191, a nucleoside analog
inhibitor of HCV RNA polymerase (NS5B) for hepatitis C, and BCX4161, an
oral inhibitor of plasma kallikrein for hereditary angioedema. Utilizing
state-of-the-art structure-guided drug design and crystallography,
BioCryst continues to discover innovative compounds with the goal of
addressing unmet medical needs of patients and physicians. For more
information, please visit the Company's website at www.BioCryst.com.

Forward-Looking Statements

This press release contains forward-looking statements, including
statements regarding future results, performance or achievements. These
statements involve known and unknown risks, uncertainties and other
factors which may cause BioCryst’s actual results, performance or
achievements to be materially different from any future results,
performances or achievements expressed or implied by the forward-looking
statements. These statements reflect our current views with respect to
future events and are based on assumptions and subject to risks and
uncertainties. Given these uncertainties, you should not place undue
reliance on these forward-looking statements. Some of the factors that
could affect the forward-looking statements contained herein include:
that BioCryst may not receive government funding to support the further
development of BCX4430; that HHS/BARDA may further condition, reduce or
eliminate future funding of the peramivir program; that BioCryst or its
licensees may not be able to enroll the required number of subjects in
planned clinical trials of its product candidates and that such clinical
trials may not be successfully completed; that the company or its
licensees may not commence as expected additional human clinical trials
with product candidates; that the FDA may require additional studies
beyond the studies planned for product candidates or may not provide
regulatory clearances which may result in delay of planned clinical
trials, clinical hold with respect to such product candidate or the lack
of market approval for such product candidate; that ongoing and future
preclinical and clinical development may not have positive results; that
the company or its licensees may not be able to continue future
development of current and future development programs; that such
development programs may never result in future product, license or
royalty payments being received; that the companies may not be able to
retain its current pharmaceutical and biotechnology partners for further
development of its product candidates or may not reach favorable
agreements with potential pharmaceutical and biotechnology partners for
further development of product candidates; that its actual cash burn
rate may not be consistent with its expectations; that 2012 operating
expenses and cash usage will be within management’s expected ranges.
Please refer to the documents BioCryst files periodically with the
Securities and Exchange Commission, specifically BioCryst’s most recent
Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and current
reports on Form 8-K, all of which identify important factors that could
cause the actual results to differ materially from those contained in
BioCryst’s projections and forward-looking statements.